Image projection apparatuses having a laser-emitting element as a light source are used as laser projectors, automotive HUDs (head-up displays), and the like. Such image projection apparatuses comprise, for example, a laser-emitting element that emits a red light, a laser-emitting element that emits a green light, and a laser-emitting element that emits a blue light and project a color image to a screen by guiding each light emitted from these laser-emitting elements to the screen.
One property of the image projection apparatuses is the wide brightness range (also referred to as wide dynamic range) of the image, which may result in stable projection. For example, when an image projection apparatus is used in an automotive HUD, if the dynamic range is wide, an image can be displayed at a brightness suited for a driver to view under any condition, for example, a condition where the intensity of an external light differs from a clear day to the night.
In a conventional laser-emitting element, a minimum drive current (a so-called threshold current) is necessary to stably perform laser oscillation. When a drive current at or above this threshold is supplied, the laser-emitting element stably emits a laser light having an intensity in accordance with an amount of the drive current. Meanwhile, when a current less than the threshold is supplied, the laser light cannot be stably emitted.
Therefore, a technology is known that performs pulse emission of the laser-emitting element by a drive current that has an amplitude at or above the threshold and whose pulse width is modulated (for example, Patent Literature 1). According to this technology, a laser light whose effective intensity is small compared to a situation in which the laser-emitting element continuously emits can be stably obtained.